The present invention relates to a method and device for performing digital frequency modulation. First, an input frequency modulation signal is converted into a digital signal via an A/D (Analogue/Digit) adapter, then a varied carrier frequency parameter "a" for each different system is added to the digital signal by an adder; next, the digital signal is multiplied by a various frequency variation parameter "b" assigned to each different system accordingly, and is further multiplied by another number 2.sup.-U, U=10 for SVHS system and U=11 for VHS system, by a multiplier; afterwards, the digital signal is processed by a digital integrator; then corresponding amplitudes in mapping with all angles .theta. and .theta.' within 360 degrees are obtained by sin.theta. ROM and Cos.theta.' ROM, wherein Z.sup.-1 is a flip-flop, the parameters "a", "b" are variable as a result of the difference in specifications of PAL, NTSC, VHS, SVHS systems and the interlace scanning so as to make the design applicable to various systems.
1. Field of the Invention
The present invention is particularly related to a method and device to reduce noise by means of digital processing of frequency modulation to integrate the image systems, such as NTSC, PAL, VHS, SVHS video recording and playing systems into a single system.
2. Related Prior Art
Conventionally, to integrate an image system, such as NTSC, PAL, VHS, SVHS video recording and playing system into a single system, it is usually designed in a bulky analogue type dimension, and the system is subject to noise interference. That is to say that the analogue type frequency modulation takes up larger space and is rather difficult to be integrated, especially difficult in control of the resolution ratio. It is particularly vital to take account of space and resistance of interference in design especially involving two or more systems so as to minimize the interference of noise signals.
Moreover, in international markets involved in a fast globalized economic system nowadays, the analogue type frequency modulation art is gradually losing its edge in competition due to the consideration of compatibility among various systems in countries all over the world which becomes unavoidable in international cooperation designs, and commercial trades and fast price drops as a result of competition on markets, and the spread of the idea of "system on chip" in the development of IC designs.
Besides, the processing of signals by an analogue type IC is not compatible with the digitalized IC designs in current and future trends. When an analogue type IC is to be integrated with a digital IC, the analogue circuit can interfere with the digital system in one aspect; and the mass production of IC components today is not supported by effective analogue testing equipment in another aspect.
To cope with the drop of price in digital IC components nowadays, an art of combining DSP (digital signal processing) and ROM to process frequency modulation and integrate various image/video recording and playing systems is developed. It intends not only to reduce the noise interference but also to increase the competitive edge of the products on markets by cutting the size and cost of commercial products.